Process for obtaining contrasts by means of diazonium compounds



UNITED STATES PATENT OFFICE PROCESS FOR OBTAIN ING-CONTBASTS BY LIEANS F DIAZONIUM COMPOUNDS Jan Hendrik De Boer, Cornelia Johannes Dippel, and Roelof Jan Hendrik Alink, Eindhoven, Netherlands, assignors to N. V. Philips Gloeilampenfabrieken, Eindhoven, Netherlands No" Drawing. Application May 19, 1932,. Serial No. 612,364. In the Netherlands May 22, 1931 Claims. (01.95-6) This invention relates to a method of obtainlight according to the invention consists in the ing photographic contrasts by means of diazouse of 'a carrier provided with a diazonium comnium compounds. The so-called diazo type is I pound (or with a plurality of such diazonium known to be based on the production of azo dyes compounds) which on exposure'in the presence of 5 by the coupling of a diazonium compound with an water forms primarily a phenol so substituted in 5 azo component and in addition to the fact that the benzene nucleus that this phenol can be oxidiazonium compounds are decomposed by exdized by the diazonium compound itself or by a posure and are thus deprived of their property further diazonium compound also'present in the of coupling with azo-components to form azocarrier to form a colored compound, the medium l0 dyes. Thus, for example, methods are known acof the carrier being such that the speed at which 10 cording to which paper provided with diazonium this oxidation process proceeds is greater than compounds is exposed under a diapositive or a 2 that at which the diazonium compound couples drawing and then treated with a solution of an with the phenol to form an azo-dye but during azo-component. The non-exposed parts are thus the exposure is smaller than that at which the coloured so that a positive of a positive is obdiazonium compound is converted by the said ex- 15, tained. A further known method involves the posure, and that the phenol is caused to be oxi use of paper containing a diazonium compound dized by the diazonium compound not yet conwhich on exposure is converted into a phenol verted t'o-form a colored oxidization product. which is then used as an azo component. In this The invention includes also almethod of obtaincase the phenols thus obtained may be caused to lug heliographic prints which is characterized 20 couple with some diazonium compound, but it is by the use of a carrier provided with a diazonium also possible to bring about a coupling with the compound which, after the local exposure and diazonium compound from which the said phewithout any other substance being added after n01 is produced. For this latter purpose it is the exposure, is caused to form a dye which is as often necessary to introduce the paper into an n t an azo-dye.

alkaline medium. If indeed an exposure through As examples of diazonium compounds suitable a negative s e So t t a the exposed p for use in carrying out the present invention we a sufiicient quantity of diazonium compound has may mention those having in the benzene nur m in .1 is p l to cause e phen l f rm cleus at least one OH-group substituted in ortho to coup e w t the di o p u Still P or para position relativelyto the diazonium 30 eht y introducing h aser a e an alkegroup. In some cases the OH-group, which in line medium. the benzene nucleus-is substituted in ortho or The method according to the invention is based para position relatively to the diazonium group, on quite a different principle: it does not utilize may be replaced by a NH: group one of the hyt coupling p p ti f dia onium omp u d drogen atoms of which may be replaced in some 35 u s bas d o t oxidizing P pe s of cases by an alkyl-, aryl-, or similar group. tain diazonium compounds. According to one embodiment of the invention The Properties n question of diazonium e diazonium compounds are used which after the p u ds will e s t ut r fu ly y reference t exposure yield polyphenols which are not adapted" 40 a e p for a p pydroxybenin any way to couple with diazonium compounds. 40 zenedlezoniumehloride is exposed (as is W The invention will now be set out more fully known there is in the usual carriers, such as pawith reference to various embodiments. per, always sumcient water to give rise to the occurrence of an OH-group) there is formed therewmi el from hydroquinone, mtrogen and hydrochloric Paper provided \with PhYdroxYbehzenediazm q accordmg to the equation: niumchloride is tlrst exposed beneatlra drawing HOCeH4N2Cl+HzQ=H0CsHiOH+N2+HCl to that part of the spectrum which is-particularly If the exposure is-made so that only part actinic relativeto the compound mentioned in this the diazonium compound present is converted example, the drawing being preferably applied to 50 to am mo 8, the am uinone is oxidized material that is readily transparentto the light 1:; z g g compohgnd form a coloured of the desired wave-band. The wave length that oxidation product. I As stated above, it is on thi is particularly actinic relatively to the compound principle that the inventio is based, mentioned in the example is in the neighbourhood '55 The method of producing contrasts by means of 'of 3009 A. The parts struck by this light first exhibit an intermediate red violet colour which on continued exposure changes to light yellow. It may be observed in this connection that this whitening of the intermediate red violet colour al'so ensues when the exposed paper is kept in daylight or even in the dark. After the said strongly actinic exposure the paper, with the drawing removed, is exposed to daylight. Daylight is much less actinic relative to the diazonium compound mentioned in this example so that there is now a question of a slightly actinic exposure. Even during this exposure the hydroquinone formed in' consequence thereof is oxidized by the diazonium compound not yet converted to form a brown coloured oxidation product so that a positive of a positive is produced. The paper above described contains a diazonium compound which on exposure yields a polyphenol that is not adapted to couple with a diazonium compound to form an azo-dye, since hydroquinone is not possessed of this property. As an alternative, the slightly actinic exposure may be obtained by short exposure to light having a high specific actinic effect relatively to the diazonium compound used or to a feeble light source producing such light. Alternatively, the action may be influenced by altering the distance of the light source.

Example 2 Paper is provided with orthohydroxybenzenediazonium chloride; otherwise, the process may be carried out similarly to Example 1. The diazonium compound used in this case differs from that mentionedin the first example in that the intermediate colour produced by the strongly actinic exposure is orange red.

According to one embodiment of the invention the stability of the paper providedwith a diazonium compound but not yet exposed may be increased by choosing as the acid residue of the diazonium compound a slightly volatile acid, such as sulphuric acid; for this purpose, preferably, a diazonium compound may be: used which contains a sulpho acid group substituted in the nucleus.

Example 3 Paper is provided with l-hydroxy-2-diazo-4- benzenesulphonic-acid. The strongly actinic exposure under a drawing is now efiected by daylight, because daylight is strongly actinic with respect to the said compound; on the contrary for the slight actinic exposure ultraviolet light may be resorted to because ultra-violet light is slightly actinic with respect to the said diazonium compound. Otherwise, the process may be efiected similarly to the above examples so that consequently also a positive of a positive is obtained. The coloured oxidation product has an orange red colour whereas the base is light yellow. In connection with the examples described the remark applies that the slightly actinic effect may be obtained by a very short exposure to the light source used for the strongly actinic exposure and then the oxidation of the phenol formed may be brought about by the diazonium compound by subsequent preservation in the dark.

In connection with the examples described it may be observed that paper normally contains suflicient water for the conversion of the diazonium compound into the phenol by the ex-' posure.

According to a particular embodiment of the invention, the oxidation reaction can be considerably accelerated by a-moderate heating, for instance to 80 C. In view of this acceleration of the oxidation reaction it is preferable that during the strongly actinic exposure the paper should be kept as cold as possible as otherwise the base is coloured too much.

Often, for obtaining a slightly actinic exposure, it is not necessary to expose on purpose as even during the manipulation such exposure is obtained spontaneously whereupon the heating may be effected.

According to a further embodiment of the invention, the formation of contrasts can be considerably promoted by means of copper salts, such as copper nitrate.

Example 4 Paper is soaked in a 0.25% alcoholic solution of 1-hydroxy-2-diazo-4-benzenesulphonic acid having added to it 0.55% of copper nitrate. After drying it is exposed under a drawing for 20 seconds to a carbon arc lamp (for'example in a heliographic printing machine), after which the drawing is removed and the paper is heated for some time to 80 0. Thus a positive of a positive in a dark grey tone is obtained.

The invention is based on the oxidation of the product produced from the diazonium compound by exposure so that for use in' carrying out the invention such diazonium compounds are particularly suitable which yield on exposure readily oxidizable products which are oxidized by the diazonium compound to form a dark-coloured oxidation product. The invention presents inter alia the advantage that the particularly suitable diazonium compounds just referred to are simple compounds having their diazonium group in a benzene nucleus. Very good contrasts may be obtained with those diazonium compounds that have an OH-group in the ortho or para position in the benzene nucleus. Alternatively, use may be made of a multiple diazotized polyamino compound which on exposure passes into a polyphenol, in which case the compound should be such that two of the diazonium groups are in ortho or para relation to each other.

As is apparent from the foregoing, the present invention permits of producing so-call'ed integral heliographic prints which obviate the need for some chemical after-treatment. A chemical after-treatment is even preferably avoided in some cases,particularly an after-treatment with alkali, such as gaseous aqua-ammonia, since in a medium of aqueous-ammonia an oxidation, by oxygen from the air, of the compounds at the spots copied out by the strongly actinic exposure ensues as well. In order to avoid this difficulty, which also occurs in the case of well-known heliographic print-papers during the aqueousammonia treatment necessary in such case'for bringing'about the coupling to form azo-dyes, it has been proposed to add beforehand'to the paper reducing compounds preventing the socalled yellowing. It is, of course, obvious that as in the case of the papers according to the invention no aqua-ammonia treatment needs to be carried out, the said reducing substances are redundant. The addition of some of such reducing substances even defeats the oxidation by the diazonium compound still present as aimed at by the invention. In addition, an aqueous Although with those compounds whichby exposure are converted into a polyphenol that cannot serve as an azo component such as hydroquinone, the oxidation reaction can be accelerated by an aqueous ammonia-treatment, this treatment has the disadvantage mentioned before that consequently the white portions subjected to the strongly actinic exposure may be oxidized by oxygen from the air so that they become darker in tone.

As mentioned above some diazonium compounds having at least one NH: group in ortho or para relation to the diazonium group in the benzene nucleus are also suitable for use in carrying out the invention. On exposure said diazonium compounds pass into an amino phenol which by the diazonium compound from which it is formed can be readily oxidized to-form a coloured oxidation product. We quote below an example of the use of such a diazonium compound.

' Example 5 Paper treated with a solution of p-phenyl aminobenzenediazonium chloride,

CeH5.HN.CeH4.NzC1,

is exposed under a drawing on transparent paper to violet light which in this case is strongly actinic, after which it is heated out of contact with the drawing to C.

In all of the examples above described it is advantageous to provide the paper unilaterally with the light sensitive substance. Thus notonly a saving in material is obtained but the reverse of the paper which naturally is only slightlyexposed is prevented from becoming dark coloured by the oxidation reaction occurring in that case.

Whenan alcoholic solution of the light sensitive substance is used for the manufacture of the heliographic print paper, the reverse side of the paper becomes light sensitive, because such a solution penetrates very quickly through the paper. The darkening of the reverse side of such paper can be avoided in that during or subsequent to the exposure also this side of the heliographic print material vis strongly exposed and preferably to such-extent that it is copied out as completely as possible. Heliographic print paper treated in this manner can therefore not receive a dark colour on its reverse side during the development of the image as a result of the copying out, as all of the diazonium compounds present thereon is converted by the light.

According to another embodiment of the invention, instead of paper other materials, such as glass, film or paper provided with a gelatine layer, may be used as the carrier of the diazonium compounds described. Such material permits of obtaining photographic prints by carrying out the invention which will beset out more fully by reference to some examples.

Example 6 converted. During the said rinsing with water, the polyphenol formed is oxidized by the excess of the diazonium compound present to form a coloured oxidation product and the greater the quantity of light that-has acted the darker are the tones. obtained, as the coloured oxidation product is insoluble. The excess of diazonium compound is washed out.

Preferably, the exposure is so effected that even at those spots upon which most of the light has fallen there remains always an excess of diazonium compound. On the contrary, an unduly prolonged exposure results in copying out and thus less dye formation or no dye formation at all can be obtained so that in the case of an excessively long exposure even anegative of a negative is obtained. If, when using the diazo- Example 7 If, instead of the'diazonium compound mentioned in example 6, l-hydrox'y-2-diazo-4-benzene sulphonic acid is used-a diazonium compound relatively to which sunlight is strongly actinicthe exposure time for obtaining photographic prints must be shorter. When a negative on glass is used, an exposure to sunlight of from 2; to min. is more than sufficient.

In contradistinction to examples 6 and 7 in which paper provided with gelatine is used as the carrier of the diazonium compounds, we shall give below an example in which a sheet of regenerated cellulose is chosen as the carrier for the diazonium compound;

, Example 8 diazonium compound, or-glass, film or paper or the like provided with a gelatine coating to which the Examples 6, 7 and 8 refer, it may be preferable that the oxidation reaction should be accelerated by bathing for a short time in aquaammonia. As in the case of these photographic uses preferably water is used for washing out and the aqua ammonia treatment is only of short duration, neither oxidation of the bottom by oxygen from the air nor coupling practically ensues in this case.

According to a particular embodiment of this photographic use the carrier may be treated, prior to its being washed out with water, with an ammoniacal copper solutlon'which obviates the need of adding copper salt to the diazonium compound of the carrier.

Even when paper not provided with a gelatine layer is used as the carrier, the washing operation with water described hereinbefore may be resorted to. If, however, in this case the wash ing operation is effected immediately after the exposure, generally vague melting images are obtained by reason of the diazonium compound being washed out too quickly relatively to the speed at which the oxidation occurs. If, therefore, it is desired to carry out the washing-out operation in the case of paper, it is preferable that after the exposure the paper should be kept for some time in the dark before it is washed out with water so as to allow time for oxidation during this preservation and consequently for the formation of dyes.

Generally, it may be observed that the durability of soaked papers is greater than that of soaked gelatine papers and Cellophane.

For the examples it will be seen that the diazonium-compounds adapted. for carrying out the invention do not group themselves according to the usual system of organic chemistry.

The invention may alsobe practised for making direct photographic exposures, in which case generally longer exposure times are used, since usually the quality of actinically active light available is smaller.

In connection with the nature of the light sensitive material referred to hereinbefore it may be advantageous, in order to obtain better contrasts, to give the carrier during the heating operation the desired degree of humidity. For this purpose it is preferable to provide the heliographic printing device with humidifying means.

According to a further embodiment of the invention it is possible to also expose the reverse of the paper so that copying out ensues there which assists in obtaining a light reverse of the paper. This may be advantageous when on being applied light sensitive substance has-reached the reverse of the paper, which occurs for example if the paper is treated with an alcoholic solution of the light sensitive substance.

It is possible to cause the exposure and the development of the light sensitive material to be brought about each in a separate device.

As has been stated, the diazonium compounds adapted for carrying out the invention do not group themselves according to the usual system of organic chemistry. However, the light-sensitive substances used are broadly light-sensitive benzene-diazonium compounds; of these a great number and variety are adapted to carry out the invention. Especially good results are obtained with p-hydroxy-benzene-diazonium-chloride; ortho hydroxy benzene diazonium chloride; 1- hydroxy-2-diazo-4-benzene sulfonic acid; p-phenolamino benzene diazonium chloride; orthophenol diazonium sulphate; and in general with such benzene-diazonium compounds in which the benzene nucleus comprises at least one OH group substituted in ortho or para position with regard to the diazonium group, or in which an NI-Iz group is similarly substituted in the benzene nucleus, or in which one of the hydrogen atoms of this NHz group is replaced by an alkyl-, aryl,

or similargroup. Such light-sensitive benzene- -dlaz'onium compounds, under proper conditions,

if subjected to suitable selective actinic exposure, will decompose at exposed portions to form a decomposition product (phenol), which, with the undecomposed diazonium compound of its surroundings, will enter into a reaction, i. e., be oxidized by the same and form a colored oxidation product, provided, dueto proper selection of the milieu of the layer, the speed of oxidation is less than the speed of decomposition (conversion) of the diazonium compound during the exposure, and provided the speed of oxidation is greater than the speed at which the decomposition product (phenol) produces, with the diazonium compound, an azo-dye. This formation of colored matter takes place to a great extent subsequent to-the actual exposure, and as a rule without further exposure or addition of any further substance after the exposure, and thus a self-development of the light-sensitive layer takes place.

In the claims the term selectively exposing should refer to the exposing of the carrier provided with a light sensitive diazonium compound, both through a suitable negative or positive.

What we claim is:

1. The process of making light prints comprising the steps, forming a light sensitive layer by applying to a carrier 2. light sensitive substance comprising a benzene-diazonium compound, selectively exposing said carrier to actinic light to partially decompose the diazonium compound at selected portions, forming a phenol and oxidizing into colored products the phenol so formed by the undecomposed diazonium compound remaining at these portions, by providing a speed of oxidation which is greater than the speed at which the benzene-diazonium compound would form an azo dye with the phenol, said selected portions forming a colored contrast with the substantially uncolored remainder of the carrier.

2. The process of making light prints comprising the steps, forming a light sensitive layer by applying to a carrier a light sensitive substance comprising a benzene-diazonium compound, selectively illuminating said layer with a strongly actinic light to partially decompose on' selected portions said diazonium compound, forming a phenol substituted in the benzene nucleus and oxidizing said phenol by non-decomposed diazonium compound at the weakly-illuminated portions at a rate which is greater than the rate at which the diazonium compound could couple with the phenol to form an azo dye, to thereby form on said weakly-illuminated portions a colored oxidation product, and photochemically decomposing during said illumination the diazonium compound at the strongly-illuminated portions at'a rate which is greater than-is the rate of oxidation of the phenol, to maintain said strongly illuminated portions substantially uncolored.

3. Process of making light prints comprising the steps, forming a light sensitive layer by applying to a carrier a light sensitive substance comprising a benzene-diazonium compound, selectively illuminating said layer with weakly actinic light to partially decompose on said selected portions said diazonium compound forming a phenol substituted in the benzene nucleus, and oxidizing said phenol by a non-decomposed diazonium comcomprising a benzene-diazonium compound, se-

lectively exposing said carrier to actinic light to partially decompose the diazonium compound at selected portions, forming a phenol in the presence of water and oxidizing into colored products the phenol so formed by the undecomposed diazonium compound remaining at these portions, by providing a speed of oxidation which is greater than the speed at which the benzene-diazonium compound would form an azo dye with the phenol, said selected portions forming a colored contrast with the substantially uncolored remainder of the carrier.

5. The method of producing a photographic print comprising the steps of providing one carrier a light sensitive benzene-diazonium compound selected from the group p-hydroxybenzenediazoniumchloride, 1 hydroxy 2'- diazo-4-benzene sulphonic acid, orthohydrobenzenediazoniumchloride, p-phenylaminobenzenediazoniuinchloride, orthophenoldiazoniumsulphate, selectively exposing said carrier to actinic light to partially decompose the diazonium compound at selected portions, forming a phenol and oxidizing into colored products'the phenol so formed by the undecomposed diazonium compound remaining at these portions, by providing a speed of oxidation which is greater than the speed at which the benzene-diazonium compound would form an azo dye with the phenol, said selected portions forming a colored contrast with the substantially uncolored remainder of the carrier.

JAN HENDRIK-DE Bonn; CORNELIS JOHANNES DIPPEL. ROELOFIJAN HENDRIK ALINK. 

